Method of drilling wells



y 19, 1942- c. M. POTTE R METHOD OF DRILLING WE LLS Filed June 2, 1941BMW/n9 F/u/d 24 l/emg Mud 27 fleal y Mud IJU eIL i501 Char/es M offer0/7/017 Flu/'0 and Cuff/'ngs I Aiiojhegy I Patented May 19, 1942 CharlesM. Potter, Taft, Calif., asslgnor to Standan! Oil Company of California,San Francisco. Calii'.,'a corporation of Delaware Application June2,1941, Serial No. 396,277

4 Claims.

This invention relates to an improved method of drilling wells withrotary equipment through cavernous or porous formations, andparticularly refers to a method of introducing two different mud-ladenfluids into the well during the drilling operations.

In the drilling of well bores, particularly those for the production ofoil and gas, porous or broken formations and sometimes actual cavernsare penetrated, some of which may carry large quantities of water thatinterferes greatly with the maintenance of an adequate hydrostatic headon the formation being penetrated, on the characteristics of thedrilling fluid, and also the disposal of the cuttings from the drillbit. If the conventional method of circulating mud fluid is used, thefluid either becomes lost in the formation or is so diluted andcontaminated by the fluids entering the well that it becomes useless forcarrying the drill cuttings to the surface. Under some circumstancessuch formations may be sealed off from the rest of the well by theintroduction of cement or various materials which will coagulate orprecipitate in the porous formation. Such treatmentsare effective wherepressures are low and the extent of the porous or cavernous formationsis limited, but occasio'nally these are of such a nature that nopractical method of sealing can be found.

This invention comprehends broadly the'utilization of the exposedcavernous formation to receive the actual drilling fluid together withthe drill cuttings from the bottom of the well bore. Under mostcircumstances it is necessary to use a second fluid as a substantiallystationary cap above the fluid which is being passed outwardly into theporous or cavernous formation. the cap serving to overcome thehydrostatic head of the water that normally flows out of that formationinto the well bore. This cap may thus be considered to float on theflowing drilling fluid, which may be water or a very thin mud. The capmaterial is usually a heavy and very viscous mud, in some cases almost agel and, in the malority of cases, may be made from water, a 001- Iloidal material, such as bentonite, and a weighting material, such asfinely ground barytes. The height of this column in the well boreobviously depends on the location of the cavernous forma-' tion, thehydrostatic pressure of the liquid in that formatiomand the pressurenecessary to put away the drilling fluid and cuttings into the cavernousor porous formation.

It is an object of this invention to provide a method of drilling wellsthrough porous or cavernous formations in which a floating mud cap isused above that formation and drillin fluid introduced through the drillpipe passes upwardly around the latter and thence outwardly through theporous formation instead of to the surface.

Another object is to provide a method of drilling wells in which a capof heavy mud is used in the upper part of the well bore to overcome highhydrostatic heads of fluid in the lower part of said bore, this capbeing substantially stationary and left in place during the introductionand withdrawal of the drill pipe and bit.

, Another object is to provide a method of drilling wells in which arelatively thin mud or water is used-for the actual drilling operations,thereby preventing the formation of mud rings in the lower part of thewell bore, and at the same time putting away the cuttings into a porousformation between the bottom of the bore and the surface of the earth.

Another object is to provide a method of drilling wells in which theso-called circulation" takes place below a stationary body of heavy mudin-the upper part of the well, thus reducing the distance through whichthe cuttings must bellfted by the circulating fluid. In this regard theword circulation may be a misnomer as the actual drilling mud is neverreturned to the surface of the ground or to the pump but is put awayinto a subsurface porous or cavernous formation. I

These and other objects and advantages of the invention will be furtherapparent from the following description and from the accompanyingdrawing which illustrates a preferred mode of application of theinvention.

The drawing is a vertical and part sectional view of a drilling wellwhich has traversed a porous or cavemous'formation into which thecuttings from the bore below that formation are to be placed.

In the drawing, reference numeral I0 illus-' trates generally the wellbore, the upper portion of which is cased by a suitable conduit II atthe upper end of which is a casinghead I2. A conventional derrickstructure It supports a rotary table l4 driven by suitable means notshown and adapted to rotate a drill pipe IS, the latter extendingdownwardly to the bottom of the well and terminating in a drill bit l6.

At the upper end of drill pipe I5 is a conventional swivel l'l providedwith bails l8 supported by the hook of a traveling block I9. A flexiblehose 20 is connected between swivel l1 and the y Among those formationswhich are penetrated by bore I is one designated 26, which is porous orcavernous, these terms being considered to be substantially equivalentin this specification. Formation 26 may or may not contain salt water orother fluid under high pressure but it is of such a nature thatsubstantial quantities of drilling fluid 24, together with the cuttingsfrom drill bit [6, may be forced into it under suitable hydrostaticpressure. In this example the hydrostatic pressure necessary to forcethe drilling fluid 24 and the cuttings into formation26 is supplied bymeans of a floating mud cap 21 in bore I0 between formation 26 and thesurface of the earth. The depth of this cap obviously the fluid 24actually used for drilling which may be entirely independent of theviscosity and weight of the mud cap material 21.

Although a single arrangement of apparatus for carrying out this methodand only one mode of procedur have been described and illustrated, it isobvious that many changes could be made without departing from theinvention and all such changes which come within the scope of dependsupon the location of formation 26, the

hydrostatic headrequired, and those other factors which will be apparentto one skilled in this art. The heavy mud 21 which comprises the mud capis desirably supplied from a separate sump 28 and is introduced atintervals as it is required by means of 'a pump 29 through valve 30 andline 3| into the side outlet 32 of casinghead l2.

It has been found that a floating mud cap of this kind is not destroyedby the introduction and removal of drillpipe l5 and drill bit I6 duringthe normal operations attendant to drilling. Also, the use of such a.cap removes the necessity for drilling under pressure or for snubbing inthe drill pipe where high hydrostatic pressures are encountered in theformations.

Another advantage that has been noted is the separate control of theviscosity and weight of the appended claims are embraced thereby.

'I claim: r

l. A method of drilling a well bore with a drill pipe and drill bitbelow cavernous or porous subsurface formations comprising the steps ofcontinuously feeding a drilling fluid downwardly through said drillpipevand bit, passing said fluid together with cuttings from said bitupwardly around said pipe withinsaid well bore, maintaining asubstantially stationary cap of heavy mud on the fluid in said bore toimpose a'predetermined hydrostatic head thereon and passing saiddrilling fluid and cuttings outwardly from said where under saidhydrostatic pressure into va cavernous or porous formation below saidcap.

2. A method of disposing of drill cuttings from -a well bore below aporous or cavernous formation comprising the steps of pumping a firstfluid into said bore below said formation, and maintaining asubstantially stationary cap of a second fluid in said bore 'abovesaidformation to impose sufiicient hydrostatic head on said first fluid tocause it to carry said cuttings into said formation. 3. A methodaccording to claim 2 in which said second fluid has a higher densitythan said-first fluid.

4. A method according to claim 2 in which said first fluid is water andsaid second fluid is a weighted mud.

CHARLES M. POTTER.

